1. Field of the Invention
The present invention relates to a liquid ejection apparatus in which a liquid ejection head having a liquid storage portion provided in a support member supporting a recording element substrate is mounted, and a liquid ejection head detachably mounted in a liquid ejection apparatus.
2. Description of the Related Art
A liquid ejection head with a plurality of liquid storage portions provided in a support member supporting a recording element substrate has been proposed (U.S. Pat. No. 7,267,431). A liquid ejection apparatus in which a liquid ejection head provided with a recording element substrate of a thermal system is mounted is described.
The recording element substrate has an ejection orifice formed in one surface of the recording element substrate, a bubbling chamber communicating with the ejection orifice, a heating resistor provided on a wall of the bubbling chamber as an ejection-energy-generating element and a plurality of liquid chambers communicating with the bubbling chamber. Each of the plural liquid chambers has an opening formed in another surface of the recording element substrate.
The support member supports said another surface. In addition, the support member has a communication path extending from the liquid storage portion to the opening of the liquid chamber. The liquid ejection head provided with the recording element substrate and the support member is mounted in the liquid ejection apparatus with the ejection orifice directed downward.
A liquid flows through the communication path and the liquid chamber in this order from the liquid storage portion to be supplied to the bubbling chamber. Film boiling is caused in the liquid within the bubbling chamber by applying drive energy to the heating resistor. The liquid is ejected from the ejection orifice by using a pressure by the film boiling.
The recording element substrate contains a relatively expensive member. In order to reduce the cost of the liquid ejection head or the liquid ejection apparatus, there is a demand for miniaturizing the recording element substrate.
For example, the recording element substrate of the thermal system contains a semiconductor substrate for forming a heating resistor and an electrical wiring electrically connected to the heating resistor. The semiconductor substrate is obtained by dividing a silicon wafer into several pieces. The silicon wafer is a disc-like plate obtained by slicing a columnar ingot grown from a seed crystal of a semiconductor material such as silicon into a predetermined thickness and is a relatively expensive member.
The semiconductor substrate can be miniaturized by miniaturizing the recording element substrate. As a result, a greater number of semiconductor substrates are obtained from one silicon wafer. In other words, the recording element substrate is miniaturized, whereby a greater number of recording element substrates are prepared from one silicon wafer to reduce the cost of the liquid ejection head or the liquid ejection apparatus.
In order to miniaturize the recording element substrate containing the plural liquid chambers, it is effective to narrow a distance between adjoining liquid chambers. In a liquid ejection head having a plurality of communication paths, it is necessary to narrow even a distance between adjoining communication paths with narrowing distance between the adjoining liquid chambers. In order to narrow the distance between the adjoining communication paths, it is considered to thin a communication path wall between the adjoining communication paths.
However, the support member having the liquid storage portion is larger than the recording element substrate. Therefore, it is desirable to mold the support member with a material cheaper and weaker than the material of the recording element substrate, such as, for example, a resin material for reducing the cost of the support member. In the case of a support member formed of a resin material, the strength of the communication path wall is insufficient when the communication path wall is thinned, whereby there is a possibility that the communication path wall may be broken upon the production of the liquid ejection head or use thereof.
In the liquid ejection head disclosed in Japanese Patent Application Laid-Open No. 2008-238518, a horizontal cross-sectional area (an area of a section when a certain substance is cut along a horizontal surface; the same shall apply to the following) of the communication path is made smaller than the area of the opening of the liquid chamber or the horizontal cross-sectional area of the liquid storage portion for such a reason. The horizontal cross-sectional area of the communication path is made smaller, whereby the thickness of the communication path wall is thickened to ensure the strength of the communication path wall.
In a liquid ejection head having plural liquid storage portions, it is desirable for the plural liquid storage portions to have different lengths (a dimension regarding liquid flow direction; the same applies hereafter) in such a manner that the liquid storage portions can be provided at relatively free positions. The plural communication paths have different lengths, whereby the plural liquid storage portions can be provided at different positions in a vertical direction.
However, when the plural communication paths in the liquid ejection head disclosed in U.S. Pat. No. 7,267,431 have different lengths, there is a possibility that a liquid may not be successfully ejected from an ejection orifice communicating with a relatively long communication path. The reason for this is described with reference to FIGS. 14A and 14B. FIGS. 14A and 14B are sectional views illustrating a liquid ejection head having a plurality of communication paths different in length from one another.
A bubble grows in a space formed of a liquid storage portion 1a, 1b or 1c, a communication path 2a, 2b or 2c and a liquid chamber 3a, 3b or 3c. This bubble is considered to be caused by a gas remaining in a liquid, air flowing in together with the liquid when the liquid is poured into the liquid storage portion 1a, 1b or 1c, air flowing in from an ejection orifice upon ejection of the liquid and air flowing in from a space between a recording element substrate 4 and a support member 5.
Buoyancy and surface tension act on the bubble. The buoyancy is upward force caused by a water head difference between an upper portion and a lower portion of the bubble. The surface tension is divided into downward force (hereinafter referred to as “upper surface tension”) acting on the upper portion of the bubble and upward force (hereinafter referred to as “lower surface tension”) acting on the lower portion of the bubble. In addition, the intensity of the surface tension depends on the surface area of the bubble, and it is known that the surface tension becomes higher as the surface area of the bubble becomes smaller.
In the liquid ejection head illustrated in FIGS. 14A and 14B, the horizontal cross-sectional area Wa of the communication path 2a is smaller than the area of the opening of the liquid chamber 3a. When a bubble 6a grows within the liquid chamber 3a, and the horizontal cross-sectional area of the bubble 6a becomes larger than the horizontal cross-sectional area Wa of the communication path 2a, only the upper portion of the bubble 6a thus enters the communication path 2a. 
Since the surface area of the upper portion of the bubble 6a is smaller than the surface area of the lower portion of the bubble 6a at this stage, the upper surface tension Tua is higher than the lower surface tension Tla. When the upper surface tension Tua becomes equal to resultant force of the lower surface tension Tla and buoyancy Ba, the bubble 6a stops going up, and the lower portion of the bubble 6a stays in the liquid chamber 3a (see FIG. 14A).
The horizontal cross-sectional area Wb of the communication path 2b is smaller than the area of the opening of the liquid chamber 3b. When a bubble 6b grows within the liquid chamber 3b, and the horizontal cross-sectional area of the bubble 6b becomes larger than the horizontal cross-sectional area Wb of the communication path 2b, the lower portion of the bubble 6b thus stays in the liquid chamber 3b, like the bubble 6a. 
FIG. 14B is a drawing illustrating a status that the bubbles 6a and 6b have further grown from the state illustrated in FIG. 14A. In the status illustrated in FIG. 14A, the upper portion of the bubble 6b staying in the communication path 2b and the liquid chamber 3b reaches the liquid storage portion 1b. Since the horizontal cross-sectional area of the liquid storage portion is larger than the horizontal cross-sectional area Wb of the communication path 2b, the surface area of the upper portion of the bubble 2b becomes larger than that in the status illustrated in FIG. 14A. As a result, the upper surface tension Tub becomes lower than the resultant force of the lower surface tension Tlb and buoyancy Bb, and so the bubble 6b rises and gets out of the liquid chamber 3b. 
Since the length La of the communication path 2a is longer than the length Lb of the communication path 2b, the upper portion of the bubble 6a does not reach the liquid storage portion 1a even when the bubble 6a has grown to the same extent as in the bubble 6b. Therefore, the upper surface tension Tua remains higher than the resultant force of the lower surface tension Tla and the buoyancy Ba, and so the lower portion of the bubble 6a continues to stay in the liquid chamber 3a. 
The grown bubble 6a hinders the flowing of the liquid to the liquid chamber 3a from the liquid storage portion 1a to incur insufficient supply of the liquid into the liquid chamber 3a. As a result, the liquid is not successfully ejected from an ejection orifice communicating with the liquid chamber 3a. 
For such a reason as described above, the liquid is not successfully ejected from the ejection orifice communicating with the relatively long communication path 2a. 
There is a proposal that a suction mechanism for sucking the bubble 6a together with the liquid in the liquid chamber 3a from the ejection orifice is provided in the liquid ejection apparatus for removing the bubble 6a in the liquid chamber 3a (Japanese Patent Application Laid-Open No. 2008-238518). When the suction mechanism is provided in the liquid ejection apparatus, however, the cost of the liquid ejection apparatus is increased.